1. Field of the Invention
The present invention relates to laser systems composed of multiple diode laser sources which are combined to yield powerful laser beams for surgery and the like. In particular, it deals with diode laser systems useful in medical applications and industrial applications, which require high power densities.
2. Information Disclosure Statement
Primarily, two types of laser systems are currently available, classical laser systems and diode laser systems. Classical laser systems are bulky and often require articulated arms to deliver laser beams to desired locations. They can be well focused at lower power levels but the size of the output spot increases along with an increase in the output power usually due to thermal lensing.
Diode lasers have certain advantages over classical lasers, such as compact size, lower power consumption and lower maintenance costs. To maintain high power densities in the output beam, however, small diameter fiberoptic delivery systems should be used with lower power emitters whereas larger diameter fibers ordinarily must be used with higher power emitters. As a practical matter, therefore, it is difficult for one to focus the output spot from many small emitters into one fiber delivery system of a given core size. The basis for the difficulty is within the properties of classical optics. A bundle of fibers, 19 fibers, for example, of a given diameter has a certain overall diameter which can only be imaged onto another diameter following optical invariants. This is known as Streibel's Law: Diameter times Sin .theta. equals a numerical constant, where Sin .theta. is a measure of the divergence of the beam emitted by a source or at a fiber's end. Sin .theta. is also a measure of the maximum acceptance angle of a fiber, i.e. it is proportional to the numerical aperture (NA) of a fiber. The larger the diameter of the bundle the greater the restriction on the minimum size of the `treatment` fiber delivering the radiation to the application site. It is impossible to achieve a smaller diameter within classical optics, then determined by Streiber's Law. Prior to the present invention, the output power of a diode laser system was controlled by the diode current. The diameter of a bundle, and hence the treatment fiber were determined by the number of diodes reaquired to achieve the desired maximum power for the system.
An ideal delivery system for many medical and industrial applications would be one which could operate with a wavelength of around 1 .mu.m at between 60 to 100 watts of output power and which would be able to provide variable power and high power density by launching into delivery fiber cores ranging from 600 .mu.m to as low as 200 .mu.m core. No existing diode laser device has achieved this goal.
When several diode lasers are combined to form a more powerful beam, for example, for medical treatment or industrial welding, the diameter of the output spot, from the several lasers, inevitably specifies a certain minimum dimension. Using present day technology, it is thus easily achievable to focus 30 W of 808 nm or 980 nm diode generated power into a 600 .mu.m output fiber core, having a numerical aperture, NA, of 0.37. While attempts are underway to achieve significantly &gt;30 W power in the same focal spot, this task still presents a challenge for production manufacturing because of the difficulty in carrying a power density at that level. Moreover, ideally, 400 .mu.m fibers or even 200 .mu.m fibers are required for certain more delicate medical interventions. On the other hand with the large bulky classical laser systems, powers of 120 W of classical laser power can currently be focused into 600 .mu.m fibers and 60 W can be focused into 400 .mu.m fibers. Thus to take full advantage of diode lasers and to compete effectively with classical laser systems, there is a need for a diode based laser system capable of meeting these requirements or improving on them.